Pumps provided with a magnetic coupling between the motor and the rotor are used for pumping liquids, such as chemicals, inflammable liquids, foodstuffs, etc. where it is required or desirable to have a completely leakproof pump.
Partly due to eddy currents in the magnetic coupling caused by the rotation of the permanent magnet and partly because of bearing and hydraulic losses the magnetic coupling may get inadmissibly hot, so that cooling becomes necessary. This is obtained in known constructions by using the pressure drop across the pump to conduct a part of the pump fluid through the coupling. This entails some disadvantages, however, in particular because the viscosities of the pump fluids are in themselves different, they are temperature dependent, and furthermore the pressure drop across the pump varies, so that there is no control of the coolant, i.e. the part of the pump fluid used for cooling. This means that the cooling of the magnetic coupling has to be individually adapted to the specific pump fluid and its temperature. The leakage of pump fluid for cooling purposes means a reduced pump capacity, and there is a pronounced risk that the calibrated opening for the coolant clogs up because of its small size.